The present invention is related to an apparatus for opening and closing doors and, more particularly, to a garage door operator with yieldable gearing and other safety mechanisms.
Garage door operators are used extensively throughout the United States of America with an estimated 20 million units in use today. Many control methods exist for reversing the drive mechanism when an obstruction is contacted during door closure. Three such methods are disclosed in U.S. Pat. No. 4,055,023 issued to G. H. Gatland et al.; U.S. Pat. No. 4,159,598 issued to G. H. Gatland et al.; and U.S. Pat. No. 4,191,237 issued to C. B. Voege. These garage door operators usually employ some mechanism for sensing obstructions through torque measurement, motor sensing, pressure switches, and the like.
Although these methods provide a degree of safety, should the sensing mechanism malfunction, the garage door operator may continue to apply force to an obstructed garage door. Thus, a clutch may be used as a torque limiter to add another degree of safety. Such a clutch mechanism is shown in U.S. Pat. No. 4,281,475 issued to V. Spandoni-Censi. However, while the clutch is slipping, force is still being applied to the obstructed garage door which can entrap a person in the closing door causing serious injury.
Present garage door operators also do not check the operational readiness of the obstruction sensing mechanism before applying force to the garage door. Thus, a detectable malfunction could result in entrapment.